A power source system with a Power Supply Unit (PSU) serving as an AC/DC (Alternating Current/Direct Current) power source is known as a power source system for a server. The power source system for a server includes a plurality of PSUs for a redundant operation or two-way power reception because a server requires high reliability.
The PSUs of the power source system perform full-wave rectification on an alternating voltage applied from an alternating-current power source, supply the full-wave rectified voltage to a primary winding of a transformer to induce a voltage across a secondary winding of the transformer, and convert the induced voltage into a direct voltage to generate a direct voltage required by the server. In the power source system for a server, power factor improvement is performed to improve efficiency which may be degraded, and thus a Power Factor Correction circuit (hereinafter referred to as a “PFC circuit”) that performs power factor improvement is provided between the input side of the PSU and the transformer. A voltage smoothing capacitor is provided between the input side of the PSU and the transformer. In the case where a current is applied to the PFC circuit when the PSU is started with an AC, a high current momentarily flows through the smoothing capacitor, and therefore an inrush current to the input section is generated.
In a power source system with a plurality of such PSUs, when the PSUs are started at the same time, inrush currents to the plurality of PSUs are generated at overlapped timing. Therefore, a high inrush current that is proportional to the number of the PSUs provided in the power source system is generated. When a power source system which normally consumes electric power of 1.5 kVA is started, for example, a high inrush current may be momentarily generated to consume electric power of more than 2 kVA.
A power source system provided with an Uninterruptible Power Supply (hereinafter referred to as a “UPS”) for security of an operation at the time of an input power failure is known. The UPS has an overcurrent protection function for protecting the UPS from an inrush current to a load device. When the overcurrent protection function of the UPS is activated, supply of electric power to the power source system is blocked.
Therefore, the power source system is provided with a UPS with a capacity that can cover a possible inrush current. For a power source system which normally consumes electric power of 1.5 kVA, for example, a UPS with a capacity of 2 kVA may not be used but a UPS that can cover electric power of up to 3 kVA should be provided if the power source system includes devices for which a high inrush current may be generated. Likewise, since a high inrush current may be generated for a power source system with a plurality of PSUs, the power source system may be connected to a power distribution switchboard with a large capacity that can cover a high current.
A power source system is disclosed in Japanese Unexamined Patent Application Publication No. 2001-169549.
However, the power source system discussed above is provided with a UPS with a large capacity or a power distribution switchboard with a large capacity to cover a high inrush current, and thus the circuit size of the power source system may be disadvantageously large.